The IEEE Std 802.1ah-2008 standard defines 3 classes of service access protection. Class I service interfaces are unprotected, Class II service interfaces provide link resiliency while Class III service interfaces represent link and node redundant service interfaces. The operation of a Class III service interface switches between access nodes within both the customer and provider networks. Therefore, protection switching over a Class III service interface always results in state changes spreading over the customer and provider networks. A Class IV service interface which in addition to the Class III capabilities provides resiliency to state changes within the networks was left as an exercise for the future.
MEF 26 introduces a standard Ethernet interconnection interface in order to make Carrier Ethernet interconnections simpler and to accelerate the global adoption of Carrier Ethernet with a standard Global Interconnection mechanism. MEF 26 specifies the reference point that is the interface between two Metro Ethernet Networks (MENs) where each operator MEN is under the control of a distinct administration authority. The External Network Network Interface (ENNI) is intended to support the extension of Ethernet services across multiple operator MENs. MEF 26 enables interconnectivity between Carrier Ethernet networks from multiple operators. The ENNI is the reference point representing the boundary between two Operator MENs that are operated as separate administrative domains so that frames can be exchanged between ENNIs of the Operator MENs.
Furthermore, MEF has specified requirements for user to network interfaces (UNI).
There is ongoing work in IEEE and in MEF to extend Ethernet network interconnect capabilities to support node redundant network interconnect that would support state change resiliency (corresponding to the “Class IV” service interface). IEEE 802.1 will define a resiliency solution for the network interconnect aimed to be applied in network network and user network interfaces.
Based on the ongoing work on IEEE and MEF, the requirements on how the data plane should work are as follows:
1) Each provider selects an external link for forwarding frames of a service independently of the peer provider's selection, i.e. the decision which external link to use for sending frames to the peer is the sole decision of the sender provider. The peer provider has to live with that choice. This service management is referred to as non-congruent service management.
2) Alternatively, the peer providers may decide to make a joint decision on the external link selection and use the same external link for sending and receiving frames. This is referred to as congruent service management.
3) If a congruent service is misconfigured, the service may appear as non-congruent. In this case, the Layer2 (L2) NI has to handle it as an ordinary non-congruent service.
There is a need to be able to forward frames between L2 NI nodes of the same provider without mixing the frames that come from or go to an external link with the frames that remain network internal. In existing solutions, this is achieved by encapsulating the frames that are either received from or destined to the ENNI. The existing solutions on service access protection are mainly suited for Class III service interfaces and do not provide protection from state changes within the different interconnected networks.
The existing solutions have the following problems. They do not provide a means for tunneling frames between the L2 NI nodes of a given provider. As a consequence, the existing solutions cannot provide the data plane for emerging new requirements. Further, they are not able to use the network internal routing protocol (e.g. Multiple Spanning Tree Protocol (MSTP)) to protect the tunnel between the L2 NI nodes. Still further, current service access protection methods cannot be used in combination with Virtual Private Local Area Network (LAN) Service (VPLS).